If the exit is visible, you can say "I see the exit over there," because you would be presently looking at the exit. If you passed the exit already, you can say "I saw the exit back there," because you are no longer facing the exit, especially if the exit is behind you. This is based on my intuition alone, and is not professional advice.

In this scenario, you can use any of the three options, but each has a slightly different nuance: "I see the exit over there." This is in the present tense and indicates that you currently have visual confirmation of the exit. It implies that you are still looking at the exit as you speak. "I saw the exit over there." This is in the past tense and implies that you had a sighting of the exit at some point in the recent past. It suggests that you might not be actively looking at the exit at the moment of speaking, but you did see it not too long ago. "I've seen the exit over there." This is in the present perfect tense and conveys that you've had the experience of seeing the exit at some undefined point in the past. It emphasizes the connection between the past experience and the present moment. You're essentially saying that you've had this experience before you started speaking and it's relevant to the current situation. All three options are grammatically correct and convey the basic idea that you've spotted the exit. The choice depends on the specific emphasis you want to give to the timing of your sighting. Since you're still in the maze, the choice of tense can reflect how recent your sighting was in relation to the current moment of communication.

You answered your question when you wrote as the scenario "I just saw the exit and would like to inform my friend . . ." Yes, you *saw* it. And, you mentioned that you are pointing in the direction of the exit. That does not matter because it is about where your eyes are looking. If you were looking at the exit, then you would say "I see the exit . . ." But since you are looking at your friend, you say "I saw . . ." "I have seen the exit" is a different kind of mood. It sounds like you are getting up onto a stage to give a speech about how you have seen the exit. There is occasion for that mood, but here you should say "I saw . . ."